1. Field of the Invention
The present invention relates to a method and device for hyperthermic treatment of tumors, more particularly to the hyperthermic treatment of tumors using a device comprising two electrodes connected to an RF source of energy and intended to be brought into contact with the patient's body for transmission of RF energy to the tumor area.
2. Description of Related Art
It is well known that hyperthermic treatment can have a beneficial effect on tumors. Descriptions of the technology have been available since the nineteenth century and it has gained ground noticeably over the last decade. Hyperthermic treatment is now established clinical routine for certain types of tumor diseases in the United States. The treatment may be local or entail heating the entire body and is based on the fact that tumorous cells are more sensitive to heat than healthy cells in certain situations. The temperatures relevant for local hyperthermy are generally in the range of 42.degree.-44.degree. C. Within this range hyperthermic treatment can kill tumorous cells whereas healthy cells will survive. Exposure times are usually from some ten minutes up to several hours or even days. The treatment is frequently repeated several times and is frequently combined with other forms of treatment such as surgery, treatment with ionizing radiation and cytostatic treatment.
The main problem will all local hyperthermic treatment, particularly the treatment of brain tumors, is the difficulty of effecting well defined and well controlled heating of exactly the relevant volume and achieving appropriate temperature gradients without the risk of producing areas with too high temperature, known as hot spots.
Several different methods are known for generating local hyperthermy, e.g., the use of heat-exchangers connected to the body in various ways, electrically heated filaments of various design for insertion into the body, dielectric heating ("short-wave"), the insertion of needle electrodes into a tumor area and connecting RF energy to these needle electrodes, conventional diathermy or monopolar or bipolar type, and microwave heating. For example, European Application No. 0 115 420 discloses a device for hyperthermia comprising a first electrode adapted to be disposed in a tract organ and a second electrode adapted to be disposed on the outer circumference of the human body so as to generate a spatially inhomogeneous electric field within the living body in cooperation with the first electrode so that a part of the living body near the first electrode may be heated more strongly than a part of the living body near the second electrode.
The present inventors previously developed a system for local hyperthermy for the treatment of brain tumors, etc., and have clinically tested the system. The prospects for patients suffering from gliomatous tumors in the brain are extremely bleak and new, unconventional therapy is therefore necessary to deal with this disease. There are some 400 cases a year in Sweden.
This clinically tested method is based on the use of a wire system comprising a DC filament and temperature sensors built into an extremely flexible casing of thin silicone rubber tubing. The tube is prepared before treatment is to be carried out and must therefore have a "finished" length and fulfill all the requirements of sterility, safety, etc. The tube is then inserted, assuming the tumor has a cavity, using stereotaxic neurosurgical methods, for instance. In other cases it can be inserted when removing the central part of the tumor by surgery. The important thing is for the tube to be wound into a ball in the cavity, thus exposing a large area to heat but being small in volume. The tube forming the ball is also used as conductor, and thus passes through the brain and out through a tunnel to an external contact. During treatment the system is connected to a control and power supply unit via this contact. The filament is heated and the temperature response can be detected via the built-in sensors. At the beginning of the heating process a cascade effect occurs in the system so that heating is greatest in the area where the tube is wound into a ball, i.e., where the density is greatest. The resistance in this part of the filament thus increases, causing even greater heating of just this part of the system.
It has been possible to achieve a relatively good hyperthermic thermal image using this method. However, it does have some weaknesses. A relatively high temperature is attained in the central part of the ball, for instance, and the heat is transported to the growth zones of the tumor and to surrounding tissue including any diffusely spread tumor cells primarily by way of conductor transport (heat diffusion). The drawback here is that a rather high central temperature must be reached in order to achieve a therapeutic temperature in regions surrounding the electrode, and this causes undesired side effects such as oedema. In animal experiments a temperature of 43.degree. C. has been documented at a distance of 4 mm from the heating system, with a central temperature of 50.degree. C. Such results show too great a thermal gradient.
The problem to be solved by the present invention is to achieve a device for hyperthermic treatment of tumors in which the heating is well controlled, ensuring that exactly the desired volume is heated to precisely the desired over-temperature as discussed above, and so that a relatively slight temperature gradient is achieved, i.e., relatively large volumes are heated to a moderate over-temperature. The situation aimed at is to achieve a temperature of approximately 42.5.degree. C. at a distance of a centimeter or so from the electrode without the central temperature becoming too high, i.e., to eliminate the above-mentioned drawbacks of high central temperature and abrupt temperature gradients.